Process for heat treating multi-component yarns

ABSTRACT

A process is disclosed for heat treating multi-component yarns which have fibers with dissimilar shrinkage properties. The multi-component yarn is heated in the absence of substantial tension on the yarn to a temperature above the shrinkage temperature of at least one component. The heated yarn is permitted to shrink without substantial yarn tension, and the yarn is subsequently cooled to set the same. The components of the yarn are rearranged within the structure of the set yarn, with the fibers possessing the greatest shrinkage rate being concentrated at the core of the yarn.

United States Patent Rendall et al.

[ Aug. 27, 1974 PROCESS FOR HEAT TREATING MULTl-COMPONENT YARNS [75] Inventors: John L. Rendall; William Q. Rhyne;

Arthur Williams, all of Greenville,

[73] Assignee: The Richen Co., Inc., Greenville,

[22] Filed: Feb. 9, 1972 [2]] Appl. No.: 224,764

[52] US. Cl. 28/72.l7 [51] Int. Cl. D02j 1/22 [58] Field of Search 28/72 HR, 72.17, 75 WT, 28/62 [56] References Cited UNITED STATES PATENTS Tradewell 28/62 Ryan 28/72 HR Eggleston 28/72.l7 X

Primary Examiner-Louis K. Rimrodt Attorney, Agent, or Firm-Lyon & Lyon [57] ABSTRACT A process is disclosed for heat treating multicomponent yarns which have fibers with dissimilar shrinkage properties. The multi-eomponent yarn is heated in the absence of substantial tension on the yarn to a temperature above the shrinkage temperature of at least one component. The heated yarn is permitted to shrink without substantial yarn tension, and the yarn is subsequently cooled to set the same. The components of the yarn are rearranged within the structure of the set yarn, with the fibers possessing the greatest shrinkage rate being concentrated at the core of the yarn.

11 Claims, 4 Drawing Figures PROCESS FOR HEAT TREATING MULTI-COMPONENT YARNS BACKGROUND OF THE INVENTION This invention relates generally as indicated to a process for heat treating multi-component yarns composed of fibers having dissimilar shrinkage properties to rearrange the components of the yarn within the yarn structure, as more particularly described hereinafter.

Yarn composed of cotton fibers is widely used in the production of various items of wearing apparel, and other articles where a surface having a soft feel is desired. It has long been recognized, however, that cotton is susceptible to breakage due to its relatively low tensile strength. To overcome this disadvantage, it is common practice to blend cotton fibers with synthetic fibers such as polyester to provide cotton yarn having sufficient strength to withstand processing such as dry cleaning or in a washing machine or dryer.

Moreover, in recent years, garments having permanent press properties have become extremely popular. Such garments are manufactured by impregnating fabric with an aqueous solution of a thermally reactive agent, forming the impregnated fabric into a garment and subsequently curing the formed garment to insolubolize the reactive agent, as described in Warnock et al; US. Pat. No. 2,974,432. Such processing, of course, imposes additional requirements upon cotton or other cellulosic fibrous material, and as the crease resistance or durable press properties are improved, the strength and abrasive resistance of the cellulose deteriorates. Accordingly, it is typically necessary to reinforce cellulosic textiles with synthetic fibers in order to counteract the loss in strength and resistance to abrasion.

Even in producing permanent press garments from fabrics of yarn consisting of blends of cellulose and synthetic fibers, however, experience has shown that an intimate blend of the synthetic and cellulose fibers is necessary in order to provide sufficient strength in the yarn for the permanent press treatment. If the fibers are not intimately blended, the yarn is not strong enough for the production of satisfactory garments. While acceptable yarn strength may thus be achieved by utilizing yarns composed of intimate blends of, for example, cotton and polyester fibers, such blends necessitate a sacrifice in terms of the surface feel of the resulting garment in that the exposed fabric surface is composed of synthetic as well as cotton fibers. Also, the appearance of knitted garments is not entirely satisfactory as it tends to resemble underwear since synthetic fibers are n ot bulky or lofty as are cotton fibers.

It is accordingly clearly desirable to have yarn formed from blends of fibers such as polyester and cotton which possess not only the necessary tensile strength but also the desirable soft surface feel of cotton and have sufficient bulk to avoid the objectionable appearance associated with knitted fabrics. It has previously been thought impractical, however, to attempt to bulk such yarn blends since the components of the blend necessarily react differently to heat and at differ ent temperatures. For example, it is quite difficult to shrink cotton without incurring degradation and at the same time cause polyester fibers to soften and shrink without becoming sticky, since polyester fibers begin to soften only at approximately 400F. whereas cotton requires careful temperature control to avoid degradation when processed at such temperatures. In the present invention, a process is provided for the production of bulked yarn composed of different fibrous compo' nents which has the above noted combination of properties.

SUMMARY OF THE INVENTION The present invention is thus directed to a process of heat treating multi-component yarns, such as yarns composed of cotton and polyester fibers, in which the yarn is heated to a temperature above the shrinkage temperature of at least one component and permitted to shrink in the absence of substantial yarn tension. The different components, having dissimilar shrinkage properties, rearrange within the yarn structure during shrinkage, such that the fibers possessing the greatest shrinkage rate (polyester fibers in the case of blends of polyester and cotton fibers) concentrate at the core of the yarn. The yarn is thereafter cooled to set the same with the fibers in the rearranged positions.

DESCRIPTION OF PREFERRED EMBODIMENTS In the drawings:

FIGS. 1 and 2 are micro-photographs of yarn composed of a blend of polyester and cotton fibers before and after treatment by the process of this invention; and

FIGS. 3 and 4 illustrate a preferred embodiment for carrying out the process of this invention, FIG. 3 being a diagrammatic framentary perspective view illustrating the general process and suitable apparatus to perform such process, and FIG. 4 being an enlarged fragmentary view illustrating a portion of the heat treating apparatus.

Referring now more particularly to FIGS. 1 and 2, the untreated polyester-cotton yarn of FIG. I is an intimate blend of polyester fibers, denoted by A, and cotton fibers denoted by B. The cotton fibers are clearly interspersed in and among the polyester fibers, and the polyester fibers likewise are dispersed throughout the yarn structure. After treatment by the process of the present invention, as shown in FIG. 2, the fibers are rearranged within the yarn structure with the polyester fibers, A, being concentrated at the core of the yarn and the cotton fibers, B, positioned about the periphery of the yarn. The cotton fibers, of course, are still intertrapped or locked in and among the polyester fibers so as to be retained securely within the yarn structure, but during shrinkage, the polyester fibers, having the greater shrinkage rate, are drawn together at the core of the yarn and thus lock the cotton fibers within the structure but at the same time leave the cotton fibers positioned about the periphery of the yarn. Such yarn, having the rearranged or reoriented structure with the polyester and cotton fibers set in the new respective positions, has the desirable attributes discussed previously, namely a surface with the soft desirable feel of cotton and the overall strength necessary for the various processing which is ordinarily obtained from a blend of cotton and polyester fibers.

As indicated previously, in order to obtain set yarn having the structure shown in FIG. 2, the multicomponent yarn is heated in the absence of substantial tension on the yarn to a temperature above the shrinkage temperature of at least one component. In the case of a polyester and cotton blend, the yarn is heated tO a minimum temperature of approximately 400F., which is slightly above the shrinkage temperature of the polyester fibers. The heated yarn is permitted to shrink also without substantial tension on the yarn which enables the components to be rearranged within the yarn structure, with the fibers processing the greatest shrinkage rate concentrated at the core of the yarn. The yarn is thereafter cooled to set the same with the fibers in the rearranged positions within the yarn structure.

Normally, only a relatively short heating time is required to effect the desired temperature elevation and shrinkage, as for example, from approximately 2 to about seconds in the instance of a blend of polyester and cotton fibers. The length of heating, however, will of course vary depending upon the particular yarn being processed and also upon the way in which the heat is applied to the yarn. In a preferred form of the process, as described in more detail hereinafter, the yarn is heated by the application of radiant heat which permits suitable processing at the temperatures and times referred to above.

As mentioned previously, cotton fibers are susceptible to degradation due to the influence of high temperature. Accordingly, in some instances, it may be desirable to impregnate the yarn with a chemical solution prior to heating to help prevent degradation of the cot ton fibers. Examples of such suitable substances include aqueous solutions of ethylene glycol and diethylene glycol. It is only necessary to use relatively small percentages of such substances, as for example, approximately one or two percent solutions. Similarly, the yarn has to take up only a sufficient quantity to keep the cotton fibers moist at the processing temperatures, and ordinarily an approximately 5 to about percent pickup of the solution during impregnation will be sufficient.

Where the multi-component yarn being processed includes cotton or other cellulosic fibers, the yarn may be impregnated with a chemical solution containing a cellulose crosslinking agent to cause the cellulose fibers to undergo crosslinking when the yarn is subsequently heated in an effort to provide additional strength to the cellulose fibers which, of course, contributes to the production of yarn having a greater overall strength. Examples of suitable such materials include aqueous solutions of commonly used cellulose crosslinking agents such as formaldehyde, urea-formaldehyde, melamine resins such as melamine formaldehyde or methylated methylol melamine resins, dimethylol dihydroxy ethylene urea (DMDHEU), etc. Such solutions will also be catalyzed with any of the usual catalysts, such as zinc nitrate, ammonium chloride, hydrochloric acid, etc. Examples of solutions which have been found acceptable are the following:

Solution No. I. 4,000 cc. water, 1,000 cc. 37 percent formaldehyde, 140 grains ammonium chloride.

Solution No. 2. 4,000 cc. water, 37 percent formaldehyde, 280 grains ammonium chloride.

Solution No. 3. 4,000 cc. water, 2,000 cc. formaldehyde (37 percent), 280 grains ammonium chloride.

Impregnation of the multi-component yarn, whether with the chemical solution to prevent degradation of cellulose fibers or with a cellulose crosslinking agent, may be achieved using any of the standard methods. Accordingly, the yarn may be impregnated by passing the same through a bath of the desired solution in continuous manner, dipping, spraying, etc.

Referring now to FIGS. 3 and 4, a preferred form of the process and apparatus for carrying out the process are illustrated. Such apparatus is the subject of copending application Ser. No. 880,744, which is assigned to the same assignee as the present application, and includes means to feed the yarn from a supply cone 1 including a feed roll 2 and a pressure roll 3. The feeding means also includes a stop motion micro-switch 4 and solenoid 5 to control movement of the yarn to stop feeding if the yarn stops moving through the apparatus. The yarn is thus fed into a nozzle designated generally by the numeral 6 (FIG. 4) enclosed within housing 7 from which it is introduced into a tubular conduit and heated as will be described. After the yarn has travelled through the heating unit, it exits through a nozzle 11 and into a cooling means 12 in which the yarn is permitted to accumulate to facilitate cooling and setting. The yarn is withdrawn from the cooling means by rewinding apparatus 14, with the rate of rewinding being correlated with the dwell time within the cooling reservoir to permit the yarn to remain within the cooling means for a sufficient time for adequate cooling and setting. As the yarn is removed from the cooling means, it is passed under bar 15 positioned adjacent to the trough 16, whereby sufficient tension is exerted on the yarn to remove snags or kinks which may have developed during cooling.

In FIG. 4, the heating unit is shown in detail. As the yarn enters the first nozzle 6, it is contacted with heated air which is injected into the nozzle through line 22. The temperature of the air injected into the nozzle 6 will, of course, vary depending upon the blend of yarn being processed but will be within the range of from approximately 200F. to about 500F. The heated air thus helps to raise the temperature of the yarn to the necessary temperature for processing and also to move the yarn through the convoluted tubular conduit while in a substantially relaxed or tensionless condition. After travelling through the tubular conduit, the yarn passes through the exit nozzle 11 and into the cooling unit 12 as previously described.

A gun type heater 30 is connected to tube 31, which connects with line 22 to inject heated air into the nozzle 6. The preheated air is fed into the gun heater through line 32, being supplied from tank 33 in which the air is introduced through line 34 by control valve 35. If desired, heating means such as a gun heater can also be connected to line 34 to heat the air supplied to the tank to assist in providing more uniform application of heat to the yarn during processing. For the same purpose, electrical heating means 36 are provided to help provide heat to the tubular conduit. Sensing means 37 is positioned in the yarn tube 38 which senses the temperature of the air passing through the yarn tube. The sensing device, of course, is connected to a control (not shown) through lead 39 and correlated with the gun heater 30 to regulate properly the temperature of air passing through the yarn tube.

The tubular conduit 21 is disposed, as shown, in a plurality of convolutions 40 about the tank 33. As the yarn passes through the tubular conduit, it is heated by the application of radiant heat from tank 33 and the electrical heating means 36. The temperature required within the convoluted conduit to shrink and bulk the yarn will vary depending upon the type of yarn being processed. With a blend of polyesters and cotton fibers, as previously described, the temperature will be at least approximately 400F, preferably approximately 425F up to about 460F or 475F. By the same token, the rate of travel of the yarn through the tubular conduit affects somewhat the temperature which is necessary to achieve the desired shrinkage and bulking (the faster the yarn travels, the higher the temperature which is necessary). The rate of travel is also variable and is dependent upon the size of the tubular conduit, the pressure of the heated air injected into the inlet nozzle and 50 to 300 yards per minute and the processing temperature from 400 to 425F. Sample No. l was a control, that is, untreated yarn included for comparison purposes.

As shown in Table 1, there was a significant gain in weight, tensile strength and elongation in the yarns treated in accordance with the present invention. The treated yarns also exhibited a uniformly smooth soft hand and compared favorably with the untreated conthe pressure differential between the inlet and outlet trol, Sample No. 1.

TABLE I NO. YPM F. SOLUTION" WET OR 120 yd. STRENGTH ELONGA- HAND & AP

DRY SKEIN (grams) TION (grains) 1 CONTROL 58 417 5 2 50 400 A WET 68 479 3 2 2 3 50 425 A WET 72 .475 315.4 3 4 50 425 DRY 72 507 316 I 5 I00 425 B WET 71.5 458 3 3 2 6 100 425 C WET 72.5 448 316 4 7 50 425 C WET 73 49l 315 4 8 300 425 C WET 74/227: 498 318.3 3 9 300 425 DRY 76/249? 454 41.5 3

[1) Bath Formulations for A, B and C as follows:

A A B C 37% Formaldehyde 1000 cc 1000 cc 2000 cc Water 4000 cc 4000 cc 4000 cc Ammonium Chloride 140 grains 280 grains 280 grains nozzles, since the yarn desirably is disposed substan- EXAMPLE 2.

tially centrally within the tubular conduit without contacting the wall. In general, in using a /3 inch diameter tubular conduit, the feed rate of the yarn will be from about 100 to about 500 yards per minute and the pressure of the injected air from about 5 to about 20 psig at the inlet nozzle and from about 2 to about .5 psig at the exit nozzle.

The exit nozzle 11 includes means designated by numeral 41 for injecting cold air into the nozzle to contact the hot yarn passing therethrough. The cold air assists in cooling and setting the yarn and normally reduces the yarn temperature from the processing temperature to approximately 125F or lower. The yarn undergoes further cooling to approximately room temperature within the cooling unit 12.

The invention will be better understood by reference to the following specific but illustrative examples.

EXAMPLE 1.

Using the general arrangement of apparatus and process previously described with respect to FIGS. 3 and 4, a blend of 60 percent polyesterpercent cotton yarn was impregnated with the indicated solution and treated under the conditions shown in Table 1, with the Using the general process and apparatus as described with respect to FIGS. 3 and 4, a blend of percent polyester-40 percent cotton yarn was processed under the conditions shown in Table 2, the yarn speed through the tubular conduit varying between 50 and 500 yards per minute and the processing temperature between 425 and 460F. The control, designated as Sample No. 1, is included for comparison.

As indicated by the results set forth in Table 2, the treated yarns each showed an increase in weight resulting from the processing of the present invention, as well as an increase in tensile strength and elongation. The results shown for Sample No. 4 are especially noteworthy in that the treated yarn was capable of 23.5 percent greater elongation than the untreated control, which is a 140 percent increase in elongation. Sample No. 4 also showed a significant increase in tensile strength of over grams and was rated the best in hand, being far superior to the untreated Sample No. 1. It is also to be noted that Sample No. 10, which was run without prior impregnation with a chemical solution at a temperature of 460F. fused, with demonstrates the necessity of careful temperature control to raise the polyester fibers above their shrinkage temperature and also avoid meltspeed of the yarn through the apparatus varying from 55 ing.

TABLE II SAMPLE YPM F. WET OR AIR PSI YD. STRENGTH ELONGA- HAND RATING" NO. DRY WT. (grams)" TION 70" (grains) Mo L Ma Average 1 59 442.7 17.1 9 9 9 9 2 50 425 DRY 10/2 73 513.1 37.0 6 8 2 5 3 300 425 DRY 10/2 73 476.4 37.0 1 2 8 4 4" 500 425 DRY 10/2 72 538.0 40.6 2 3 1 2 5 300 425 WET 10/2 71 513.8 36.3 4 6 8 6 6 500 425 WET 12/2 70 490.0 37.8 5 5 3 4 7 500 440 WET 12/2 70 491.2 38.9 3 1 4 3 8 500 460 WET 12/2 73 455.6 37.2 7 4 6 6 TABLE II -Continued SAMPLE YPM F. WET OR AIR PSI I20 YD. STRENGTH ELONGA- HAND RATING NO. DRY WT. (grams) TION /c" (grains) Mo L Ma Average 9 500 440 DRY 12/2 75 514.5 4L6 8 7 7 7 I 500 460 DRY 12/2 Fusing 410.7 487 "'Description of lnstron Used B Cell IO Gage 6.0"lmin X hd sp l2.0"/min chart sp I000 grams FSL 'S lb. cones run on 2/4/71 and same skein weight EXAMPLE 3.

An open end spun yarn of a 75/25 percent polyestercotton blend having a yarn number of 24.2/1 was passed through the heaters of a Scragg texturizing machine, set at a minimum temperature of 210C, at a speed of 102 yards per minute. The false twist device was eliminated, and the yarn was passed only through heaters. The yarn was then conditioned for 72 hours and the properties of the yarn were examined. An untreated yarn from the same source was also conditioned and tested in a similar manner.

The average breaking load and percent elongation together with percent of the coefficient of variation and standard deviation were obtained using an Ulster Dynamometer at a full scale load of 1,000 grams and 40 percent elongation. The rate of loading was kept at 6,000 grams per minute, and 100 tests were carried out.

Tendency to curl As shown in the foregoing table, the tenacity and average breaking strength of the yarn were increased considerably by the described treatment. Also, the appearance of the yarn was improved by the heat treatment, and the tendency of the yarn to curl was eliminated.

Although the invention has been described specifically with respect to yarns composed of polyester and cotton fibers, it is applicable to various blends of yarns in which the components have dissimilar shrinkage properties such that one component shrinks at a faster rate than the other components to produce the described concentration at the core of the yarn. Illustrative examples of other multi-component yarns include blends of polyolefin and cotton, polyester and other cellulosic fibers such as rayon, and blends of polyester, cotton and wool fibers. In general, there is no minimum quantity of any single fiber which must be present in the blend, as practical considerations based on the intended ultimate use of the fabrics will dictate the percent of the various components which must be present. In the case of blends of polyester and cotton, for exam- "lndividual Raters Mo Mohamed L Lord Ma Massey *Solution Formulation obtained (18% shrinkage).

ple, the polyester content will normally be within the range of from about 10 to about 90 percent by weight based on the total weight of the yarn, with a preferred polyester content being within the range of about 20 to about 80 percent. When the yarn is ultimately to be processed into permanent garments, the minimum polyester content will normally be somewhat greater, as for example, from 40 to percent.

Yarns processed in accordance with the present invention have many uses, including the production of knitted fabrics and garments produced therefrom, various items of wearing apparel, sheets, pillow cases, shag carpets or any other use where the type of yarn surface is important, that is, where a soft surface is desirable.

Other processing may also be utilized in conjunction with the process of the present invention. For example, graft copolymers may be prepared by the injection of an inert gas such as nitrogen into the yarn tube (the embodiment of FIGS. 3 and 4) along with a gaseous monomer such as an acrylic monomer and the heated air. Similarly, gases may be injected with the heated air to create sites within the yarn to enhance the moisture re gain, dyeability and soil release properties. It is also possible to apply a coating around the fibers to affect the flameability of the yarn.

The process of this invention thus causes a rearrangement of the fibers within the yarn structure in such a way to cause certain fibers to move to the core. This is believed to be due to a relaxation of the yarn structure occurring when the yarn is heated in the absence of substantial yarn tension which releases the locked-in stresses in the fibers and yarn. Since the yarn is not held under tension during processing, the fibers are free to move within the yarn structure when heat is applied, with the fibers having the greatest shrinkage rate concentrating at the core. The release of stress is of particular significance where the yarn is to be knitted, in which case yarns have recoverable torsional strains which are likely to cause trouble during knitting as well as in the final knitted structure. Also, due to the fiber movement within the yarn structure, a variety of differential core structures can be formed and a preformed fiber component can be brought to the surface of the yarn to give the yarn the desired physical and aesthetic qualities. By the same token, the yarn may be subjected to periodic variations in treatment conditions to provide varying degrees of shrinkage and bulking as desired throughout the length of the yarn. When such yarn is dyed, the areas of varying bulk will react differently to provide a yarn having a fancy appearance. Also, the fiber forming the core of the set yarn can be of a different color than the fibers forming the periphery to give a tweedy appearance to the yarn.

We claim:

1. A continuous process of heat treating multicomponent yarns composed of a blend of natural and synthetic fibers, said synthetic fibers having a greater shrinkage capability than said natural fibers, comprising passing such multi-component yarn through a noz' zle and a tubular convoluted conduit positioned at the exit end of said nozzle, contacting said yarn within said nozzle with heated air to cause said yarn to pass through said nozzle and through said tubular conduit, further heating said multi-component yarn within said tubular conduit with dry heat to a temperature above the shrinkage temperature of said synthetic fibers in'the absence of substantial tension on the yarn, permitting said heated yarn to shrink without substantial tension on said yarn whereby said fibers rearrange within the yarn structure with the synthetic fibers concentrating at the core thereof to provide strength to the yarn and the natural fibers being positioned about the periphery of said yarn to provide a soft surface feel to the yarn, and subsequently removing said yarn from said tubular conduit and cooling said yarn to set the same with the fibers in such rearranged positions within said yarn.

2. The process of claim 1 in which said multicomponent yarn is a blend of polyester and cotton fibers, and said polyester fibers are concentrated at the core and said cotton fibers are positioned about the periphery of said set yarn.

3. The process of claim 2 in which said yarn blend contains from about 10 percent by weight to about 90 percent by weight of polyester fibers.

4. The process of claim 2 in which said yarn is heated to a temperature of at least approximately 400F. for approximately 5 to seconds.

5. The process of claim 2 in which said multicornponent yarn is impregnated with a chemical solution prior to heating to help prevent degradation of said cotton fibers.

6. The process of claim 2 in which said multicomponent yarn is impregnated with a chemical solution containing a cellulose crosslinking agent whereby said cotton fibers undergo crosslinking when said multicomponent yarn is subsequently heated.

7. The process of claim 6 in which said multicomponent yarn is impregnated with a catalyzed formaldehyde solution.

8. A process of heat treating multicomponent yarns having fibers with dissimilar shrinkage properties and composed of a blend of natural and synthetic fibers, said synthetic fibers having a greater shrinkage capability than said natural fibers, comprising passing said yarn through a first nozzle and a tubular convoluted conduit positioned at the exit end of said first nozzle, contacting said yarn within said first nozzle with heated air to cause said yarn to pass through said nozzle and through said tubular conduit, further heating said mul ti-component yarn within said tubular conduit by the application of radiant heat to a temperature above the shrinkage temperature of said synthetic fibers of said yarn in the absence of substantial tension on said yarn, permitting said heated yarn to shrink without substantial tension on said yarn whereby said fibers are rearranged within the yarn structure with the synthetic fibers concentrating at the core thereof to provide strength to the yarn and the natural fibers being positioned about the periphery of said yarn to provide a soft surface feel to the yarn, and subsequently removing said yarn from said tubular conduit, passing said yarn through a second nozzle and contacting said yarn with cold air within said second nozzle to cool the same and to facilitate setting of the yarn with said fibers in such rearranged position within said yarn.

9. The process of claim 8 in which said multicomponent yarn is a blend of polyester and cotton fibers and said yarn is heated to a temperature of at least 400F. for from approximately 5 to 10 seconds, said polyester fibers being concentrated at the core and said cotton fibers positioned about the periphery of said set yarn.

10. The process of claim 8 in which said heated air injected into said first nozzle is at a temperature of approximately 200 to about 500]F. and a pressure of about approximately 5 to about 20 psig.

11. The process of claim 8 in which said multicomponent yarn is passed through said nozzle and tubular conduit at a speed of approximately to about 400 yards per minute. 

1. A continuous process of heat treating multi-component yarns composed of a blend of natural and synthetic fibers, said synthetic fibers having a greater shrinkage capability than said natural fibers, comprising passing such multi-component yarn through a nozzle and a tubular convoluted conduit positioned at the exit end of said nozzle, contacting said yarn within said nozzle with heated air to cause said yarn to pass through said nozzle and through said tubular conduit, further heating said multi-component yarn within said tubular conduit with dry heat to a temperature above the shrinkage temperature of said synthetic fibers in the absence of substantial tension on the yarn, permitting said heated yarn to shrink without substantial tension on said yarn whereby said fibers rearrange within the yarn structure with the synthetic fibers concentrating at the core thereof to provide strength to the yarn and the natural fibers being positioned about the periphery of said yarn to provide a soft surface feel to the yarn, and subsequently removing said yarn from said tubular conduit and cooling said yarn to set the same with the fibers in such rearranged positions within said yarn.
 2. The process of claim 1 in which said multicomponent yarn is a blend of polyester and cotton fibers, and said polyester fibers are concentrated at the core and said cotton fibers are positioned about the periphery of said set yarn.
 3. The process of claim 2 in which said yarn blend contains from about 10 percent by weight to about 90 percent by weight of polyester fibers.
 4. The process of claim 2 in which said yarn is heated to a temperature of at least approximately 400*F. for approximately 5 to 10 seconds.
 5. The process of claim 2 in which said multicomponent yarn is impregnated with a chemical solution prior to heating to help prevent degradation of said cotton fibers.
 6. The process of claim 2 in which said multicomponent yarn is impregnated with a chemical solution containing a cellulose crosslinking agent whereby said cotton fibers undergo crosslinking when said multi-component yarn is subsequently heated.
 7. The process of claim 6 in which said multicomponent yarn is impregnated with a catalyzed formaldehyde solution.
 8. A process of heat treating multicomponent yarns having fibers with dissimilar shrinkage properties and composed of a blend of natural and synthetic fibers, said synthetic fibers having a greater shrinkage capability than said natural fibers, comprising passing said yarn through a first nozzle and a tubular convoluted conduit positioned at the exit end of said first nozzle, contacting said yarn within said first nozzle with heated air to cause said yarn to pass through said nozzle and through said tubular conduit, further heating said multi-component yarn within said tubular conduit by the application of radiant heat to a temperature above the shrinkage temperature of said synthetic fibers of said yarn in the absence of substantial tension on said yarn, permitting said heated yarn to shrink without substantial tension on said yarn whereby said fibers are rearranged within the yarn structure with the synthetic fibers concentrating at the core thereof to provide strength to the yarn and the natural fibers being positioned about the periphery of said yarn to provide a soft surface feel to the yarn, and subsequently removing said yarn from said tubular conduit, passing said yarn through a second nozzle and contacting said yarn with cold air within said second nozzle to cool the same and to facilitate setting of the yarn with said fibers in such rearranged position within said yarn.
 9. The process of claim 8 in which said multicomponent yarn is a blend of polyester and cotton fibers and said yarn is heated to a temperature of at least 400*F. for from approximately 5 to 10 seconds, said polyester fibers being concentrated at the core and said cotton fibers positioned about the periphery of said set yarn.
 10. The process of claim 8 in which said heated air injected into said first nozzle is at a temperature of approximately 200* to about 500*F. and a pressure of about approximately 5 to about 20 psig.
 11. The process of claim 8 in which said multicomponent yarn is passed through said nozzle and tubular conduit at a speed of approximately 100 to about 400 yards per minute. 